Mitsubishi GX Configurator-PT, User Manual

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MELSEC-Q
1 PRODUCT OUTLINE
1.1.3 Outline design of positioning control system
The outline of the positioning control system operation and design, using the QD70, is
shown below.
(1) Positioning control system using QD70
Positioning module
QD70
PLC CPU
M
PG
GX Configurator-PT
Program
Intelligent
function module
parameter
Read, write, etc.
Monitor date read
Initial setteng /Auto rofresh setting/Monitor
Drive unit
Buffer
memories
/XY
device
Forward run
pulse train
Reverse run
pulse train
Deviation
counter
D/A
converter
Speed
command
Servo
amplifiter
Interface
Feedback pulse
Servomotor
Fig. 1.2 Outline of the operation of positioning control system using QD70
(a) Positioning operation by the QD70
1) The QD70 output is a pulse train.
The pulse train output by the QD70 is counted by and stored in the
deviation counter in the drive unit.
The D/A converter outputs an analog DC current proportionate to the
count maintained by the deviation counter (called "pulse droop"). The
analog DC current serves as the servo motor speed control signal.
2) The servo motor rotation is controlled by the speed control signal from
the drive unit.
As the servo motor rotates, the pulse generator (PG) attached to the
servo motor generates feedback pulses, the frequency of which is
proportionate to the rotation speed.
The feedback pulses are fed back to the drive unit and decrements the
pulse droop, the pulse count maintained by the deviation counter.
The motor keeps on rotating as the pulse droop is maintained at a
certain level.
3) When the QD70 terminates the output of a pulse train, the servo motor
decelerates as the pulse droop decreases and stops when the count
drops to zero.
Thus, the servo motor rotation speed is proportionate to the pulse
frequency, while the overall motor rotation angle is proportionate to the
total number of pulses output by the QD70.
Therefore, when a movement amount per pulse is given, the overall
movement amount can be determined by the number of pulses in the
pulse train.
The pulse frequency, on the other hand, determines the servo motor
rotation speed (feed speed).